Question

What is the equation for experimental variance used in Type-A evaluation of uncertainty?

(a) σ = √[(1/n-1) ∑^ni=1 (xi-x’)].

(b) σ = √[(1/n-1) ∑^ni=1 (xi-x’)^2].

(c) σ = √[(1/n-1) ∑^ni=1 (xi+x’)^2].

(d) σ = √[(1/n+1) ∑^ni=1 (xi-x’)].

I got this question at a job interview.

Asked question is from Type A Evaluation of Uncertainty in portion Evaluating Uncertainty in Measurement of Engineering Metrology

Answer 1

Right answer is (b) σ = √[(1/n-1) ∑^ni=1 (xi-x’)^2].

To explain I would say: Standard deviation is basically the measurement of the dispersion of a data set from its average. Formula is given by, σ = √[(1/n-1) ∑^ni=1 (xi-x’)^2], where x’ is arithmetic mean and is equal to [(1/n) ∑^ni=1 (xi)].